1. Field of the Invention
The present invention relates to a viewfinder optical system for a camera, and more particularly to a viewfinder optical system of an inverted Galilean type which has great magnification relative to the diameter of the objective lens component.
2. Description of the Prior Art
Most viewfinder optical systems of recent lens-shutter cameras are of the inverted Galilean type. One example of this type is shown in FIG. 5. It includes basically two lens units with one lens component for each consisting of, from the object side, an objective lens component (Lo) having a negative refractive power and an eyepiece lens component (Le) having a positive refractive power. The construction is very simple and advantageously inexpensive. This viewfinder optical system of an inverted Galilean type, however, has a disadvantage in that the diameter of the objective lens component becomes greater, as the magnification becomes greater. It is a recent trend to incorporate a flash device, a range finder and so on into a lens-shutter camera near the viewfinder, causing the decrease in the space for the viewfinder system. As the diameter of the objective lens component should be kept small, the magnification of the viewfinder optical system tends to decrease.
In order to make the magnification greater without widening the space for the viewfinder optical system, it has been proposed to arrange a thick parallel glass block (Lb) between the objective lens component (Lo) and the eyepiece lens component (Le). Such a construction is shown in FIG. 6. With this construction, the total length of the whole viewfinder optical system becomes shorter while the magnification becomes greater. But the use of the parallel glass block (Lb) causes an increase in the number of parts, and thus an increase in manufacturing costs.